Device-to-device communication (D2D communication) is communication in which two or more terminal devices transmit and receive signals directly, unlike typical cellular communication in which a base station and a terminal device transmit and receive signals. For this reason, it is anticipated that D2D communication will be used to create new usage scenarios for terminal devices that differ from the typical cellular communication above. For example, various applications are conceivable, such as information sharing by data communication between nearby terminal devices or among a group of nearby terminal devices, distribution of information from an installed terminal device, and autonomous communication between machines, called machine-to-machine (M2M) communication.
Additionally, it is conceivable that D2D communication will be put to effective use in data offloading in response to the significant increase in data traffic due to the recent increase in smartphones. For example, in recent years, there has been a sharp rise in the necessity to transmit and receive video image streaming data. However, since video images typically have large data sizes, there is a problem of consuming many resources on a radio access network (RAN). Consequently, if terminal devices are in a state suitable for D2D communication with each other, such as when the terminal devices are a short distance away from each other, video image data may be offloaded to D2D communication, thereby moderating the resource consumption and processing load on a RAN. In this way, D2D communication provides value to both telecommunications carriers and users. For this reason, D2D communication is currently recognized as one crucial technology area for Long Term Evolution (LTE), and is receiving attention from the 3rd Generation Partnership Project (3GPP) standards committee.
For example, Non Patent Literature 1 discloses technology such as synchronization and discovery of D2D communication.